PROJECT SUMMARY Microvascular remodeling is an important contributor to vascular disease. Our team is broadly interested in how the extracellular matrix (ECM) affects microvascular function, and we are poised to make important contributions in this area to improve mechanistic understanding of human ascending aortic disease. The long-term goal of our work is to develop better strategies to diagnose and treat the over 2.5 million people affected worldwide by dissection and/or rupture of thoracic aortic aneurysm (TAA). We demonstrated that deficiency in angiogenic factors and collagen immaturity in the adventitial ECM are associated with vasa vasorum remodeling in degenerative and bicuspid aortic valve-associated TAA. These noted adventitial ECM disruptions in TAA helped to shape our central hypothesis that matrix cues in TAA provoke vasa vasorum dysfunction. Preliminary studies by our team revealed that hydrogel bioscaffolds made from adventitial ECM recapitulate native microstructure and retain signaling cues that invoke angiogenesis in vivo and endothelial cell proliferation and formation of branched networks in vitro. We will use human aortic tissue from early stages and multiple etiologies of TAA and porcine arteries to prepare ECM bioscaffolds from these tissues as biomimetic matrices of healthy and disease microenvironments. This approach optimally tests our central hypothesis at the whole vessel and cellular levels through execution of two specific aims. Aim 1) Determine how extracellular matrix of TAA affects remodeling and endothelial function of vasa vasorum; and Aim 2) Identify what matrix signals are necessary for regeneration of functional vasa vasorum. Under the first aim, we will comprehensively characterize the adventitial matrix of healthy aorta and various stages of human aneurysmal disease. We will then use ECM bioscaffolds derived from these human tissues to determine how matrix cues impact remodeling and endothelial function in isolated whole vessels of vasa vasorum and primary cultured human endothelial cells. Under the second aim, we will identify what growth factor-dependent and independent matrix cues regenerate functional vasa vasorum by pericytes isolated from TAA using in vitro and in vivo techniques. What we learn about vasa vasorum function in TAA could lead to the development of novel diagnostic approach that measure in vivo microvascular function in patients. Because aortic replacement remains the only treatment for ascending TAA, our work addresses an unmet clinical need to develop better therapies for TAA. Ultimately, the proposed research aspires to yield translational methods to understand, diagnose, and treat TAA, and therefore, improve patient-specific risk mitigation for aortic catastrophe. These approaches are innovative because they focus on aortic disease from perspective of the adventitial matrix which could lead to development of novel medicinal and regenerative medicine therapies and could help develop improved diagnostic measures for TAA.